The present invention relates to an implantable defibrillator output circuit, and more specifically to an output bridge circuit for issuing mono-phasic, multi-phasic, and sequential defibrillation pulses.
In the field of implantable defibrillators, it has been found that a bi-phasic defibrillation pulse applied to a fibrillating heart is useful in controlling and arresting ventricular fibrillation. See for example, commonly assigned U.S. patent application Ser. No. 143,061, filed Jan. 12, 1988, and entitled BI-PHASIC PULSE GENERATOR FOR AN IMPLANTABLE DEFIBRILLATOR. This application discloses a circuit for generating a bi-phasic voltage pulse, the circuit including first and second thyristors for regulating the voltage of a capacitor. The circuit further includes an output sensing section for sensing the exponential decay of the capacitor and signalling a control circuit to switch metal oxide silicon insulated gate transistors (MOSIGT) in a ground circuit such that after one thyristor applies a voltage pulse to the heart in a first polarity the control circuit interrupts to turn off the thyristor. The other thyristor then applies the voltage pulse to the heart in a second and opposite polarity. It, in turn, is turned off by a second MOSIGT. While this disclosed circuit is capable of generating a bi-phasic defibrillation pulse, the ground return terminal needs to be disconnected in order to commutate the current flow through the electrodes to the heart.